This invention relates generally to track formats for computer disk drives.
Disk drive systems store data magnetically, often in multiple disks each having two storage surfaces. Bytes of information are stored on these surfaces as binary ones and zeros. In order to efficiently store and retrieve bytes of information stored on such disks, disk drive controllers need to know locations on the disk where to write data to and read data from the disk. Each location on a disk is identified, therefore, by short segments of site information stored at various locations on the disk surface. Using this site information, the disk drive can accurately store data to, and retrieve data from, desired locations on the disk surfaces.
Data are stored in multiple concentric circular tracks on one or more surfaces of the disk. On each track are spoke areas separated by user data areas. The spoke areas generally include a spoke number field to discriminate one spoke on a track from another. The information in the spoke number field is used to establish a position of the disk relative to magnetic heads in the disk drive that are used to read and write the disk surface. Techniques which have been used to produce a spoke number include providing a whole spoke number in each spoke field to provide a straightforward technique to identify angular position anywhere on the track. Another technique uses a portion of the full spoke number, such as an N number of LSB's of the spoke number, in each spoke field. This arrangement also requires that certain spoke fields have a uniquely formatted index spoke in order to fully identify the position of any spoke field when angular position context is lost in the disk drive. The provision of uniquely formatted index spokes are needed since using an N number of bits in the spoke field will result in an ambiguous identification of a spoke beyond a range of 2.sup.n spokes.